PWM Solar Controller: Pros and Cons

This article explores the pros and cons of PWM (Pulse Width Modulation) solar charge controllers, contrasting them with MPPT (Maximum Power Point Tracking) controllers. These controllers are essential for regulating the flow of electricity from solar panels to batteries, preventing overcharging and deep discharging.

What is a PWM Solar Controller?

PWM stands for Pulse Width Modulation (or Pulse Duration Modulation). It essentially acts as an electronic switch, controlling the average voltage (or current) delivered to the battery by rapidly switching the connection between the solar panel and the battery on and off. The “duty cycle” (the percentage of time the switch is “on”) determines the average voltage.

During normal charging, the PWM controller allows the solar panel to deliver as much current as needed to the battery. However, once the battery reaches its target voltage, the PWM controller disconnects the panel to prevent overcharging.

The output voltage from a PWM controller can be calculated as follows:

V_out = V_max * Duty cycle (%)

Where:

• Duty Cycle (%) = [ T_ON /(T_ON +T_OFF ) ]*100
• T_ON + T_OFF = period of the pulse width modulated waveform (1/Frequency).

As illustrated, PWM charge controllers operate near the maximum power point, although typically slightly above it. They’re generally cheaper and smaller than MPPT controllers. Low-pass filters (often RC circuits) are used to smooth the PWM output into a stable DC voltage. The simpler design of PWM controllers often translates to a longer lifespan. Furthermore, most modern microcontrollers include PWM capabilities, simplifying the development of PWM solar charge controllers.

For a comparison of PWM and MPPT controllers, refer to a dedicated resource on the differences between PWM and MPPT solar charge controllers.

The image above shows a typical PWM solar charge controller.

Here are some typical specifications of a Luminous PWM solar charge controller:

• Model: SCC1220NM, 20 Amp
• Automatic Selection: 12V/24V battery
• Efficiency: 98%
• Protection: Microcontroller-based software protections
• Battery Type: Option to select SMF (Sealed Maintenance Free) and lead-acid battery

Advantages of PWM Solar Controllers

Here are the key benefits of using PWM solar charge controllers:

• Cost-Effective: They are less expensive compared to MPPT solar charge controllers.
• Compact Size: Their smaller size makes them easier to handle and install.
• Long Lifespan: Fewer electronic components and reduced thermal stress contribute to a longer lifespan.
• Suitable for Smaller Systems: They’re ideal for smaller systems where the voltage difference between the solar panel output and the battery voltage is minimal.

Disadvantages of PWM Solar Controllers

Here are the limitations of using PWM solar charge controllers:

• Lower Efficiency: They are less efficient than MPPT solar controllers.
• Limited Output: They generate less output and support lower current capacities.
• Lack of Optimization: They cannot optimize for voltage differences or load variations.
• Not Suitable for Larger Systems: They are not suitable for larger systems or situations where the solar panel output voltage is significantly higher than the battery voltage.